Iron-nitride-carbide powder and method for its production



. 4 IRQN-NITRIBil-CE PGWDER AND METHGD FOR ITS PRGDUQT@N Harry Kioepfer, Frankfurt am Main, Johannes Miiiler, Near-lsenburg, and Fritz Spar-r, Frankfurt am Main, Germany, assignors to Deutsche Goidand Silber- Scheideanstalt vormals Roessler, Frankfurt am Main, Germany No Drawing; FiledFeb; 8, 1563, Ser. No. 257,086 Claims priority, application, Germany, Feb. 13, 1962,

D 33,140 7 Claims. eras-uses The present invention relates to an iron-nitride-carbide powder which is especially suited for use in the production of sintered iron bodies of good strength and high resistance to wear, as well as of good conductivity.

It is known in the production of sintered iron bodies with the above-mentioned properties to admix with the iron powder employed a similar iron powder which has undergone a heat treatment with a medium yielding nitro gen. In such known process a sutlicient quantity of the heat treated nitrided iron powder is admixed with the soft iron powder that the nitrogen content of the total mixture is up to 0.8% prior to shaping such powders by compression molding and the like. It was proposed to employ a nitrided powder with a nitrogen content of at least 7% in preparing such admixture as it was considered desirable to keep the quantity of such nitrided powder with respect to the total nitrogen content of the mixture desired as low as possible in order that the quantity of soft iron powder which to a certain extent forms a matrix for the nitrided powder be kept as high as possible so that the pressing and sintering properties of the mixtures are not substantially less favorable than of pure soft iron powder.

It was, however, found that the processing properties of such mixtures, as well as the mechanical properties of the finished shaped and sintered bodies, do not only depend upon the total amount of nitrogen in the mixture but also that the nitrogen content and structure of the nitrided powder component plays a substantial role in the improvement of the Sintered bodies produced, and that a high nitrogen content in no way leads to the optimum results.

According to the invention it was unexpectedly found that an iron-nitride-carbide powder with a maximum nitrogen content of 7%, preferably 46%, a carbon content of 1-3%, preferably 1.82%, and containing the nitrogen essentially or entirely in the E-iron nitride phase is admirably suited for purposes indicated above. A further important requirement for the effective use of the iron nitride powder according to the invention for improving the mechanical properties and the sintering properties of iron/iron-nitride-carbide powder mixtures is that the nitrided component is practically free of when. These characteristics of such an iron-nitride-carbide powder can be easily ascertained and checked by X-ray analysis. Es pecially good results are obtained with iron-nitride-carbide powders having a 4 to 6% nitrogen content. it was previously not known that iron nitrogen alloys could be prepared with such a low nitrogen content, wherein the nitrogen content is only in the f-phase and whose X-ray picture show neither an a-iron phase nor a 'y-phase. Preferably the ratio of carbon to nitrogen is about 1:3. The ironnitride-carbide powder according to the invention can be produced by nitriding in fused cyanate containing salt baths. However, practical difficulties are encountered in introducing the untreated iron powder into the fused salt baths because the iron powder is not easily wetted by the fused salt and consequently tends to the formation of agglomerates and lumps which the salt has difficulty in penetrating and, as a consequence, a uniform and rapid action on the individual iron particles is not always as- 3,l45,45d Patented Aug. 25', 1964 mass and the nitrided powder separated from the solution and dried.

It is especially advantageous only to employ acyanate' as the nitriding salt in the production of the iron-nitridecarbide powders according ot-the invention as then the solutions obtained upon washing the treated iron powders are not poisonous or at least considerably less poisonous than the solutions which are obtained when cyanide cyanate mixtures are used. In addition, when cyanate is used alone the nitriding can be effected in a considerably shorter time, for example, in about 15 minutes. Furthermore, it was found that the nitriding of a mixture of iron powder and cyanate provides an extraordinarily good assurance of providing the desired nitrogen and carbon contents, the freedom from a-phase and that the nitrogen content is practically quantitatively only in the g-iron nitride phase.

The nitrogen content can be adjusted by changing the cyanide cyanate ratio. Pure cyanate, for example, will provide a nitrogen content of about 5.5% by weight with a nitriding time of 15-30 minutes. A mixture of cyanate and 15% cyanide provides a nitrogen content of about 4.5% with the same carbon content with a nitriding time of about 2-3 hours.

The following examples will serve to illustrate the invention with reference to several specific embodiments thereof.

Example 1 6 kg. of iron powder with an average grain size of 40 60 were carefully mixed with 7 kg. of a salt mixture of 15% of sodium cyanide and 85% of potassium cyanate and such mixture heated in an iron crucible in an electric furnace for 2.5 hours at 570 C. After cooling down the resulting salt cake was treated with water until all of the salt was washed out. 6.4 kg. of nitrided iron powder with a nitrogen content of 4.5% and a carbon content of 1.8% were obtained. Upon X-ray analysis only s-iron nitride and no a-iron could be ascertained.

Example 2 7 kg. of iron powder with an average grain size of 40-60 were carefully mixed with 7 kilograms of pota sium cyanate and such mixture heated in an iron crucible for 30 minutes at 570 C. in an electric furnace. After cooling down the resulting salt cake was treated with water until all of the salt was washed out. 7.5 kg. of nitrided iron powder with a nitrogen content of 5.5% and a carbon content of 1.9% were obtained. Upon X-ray analysis again only .i-iron nitride and no ct-ilOtl could be ascertained.

The iron-nitride-carbide powders according to the in- We claim:

1. Iron-nitride-carbide powder the individual particles of which have a carbon content of 1-3% by weight and a maximum nitrogen content of 7% by weight, said ironnitride-carbide powder being free of a-rion and having the nitrogen content essentially only in the E-iron nitride phase.

2. The iron-nitrid'e-c'arbide powder according to claim 1 in which the ratio of carbon to nitrogen is about 1:3.

3. The iron-nitride-carbide powder according to claim 1 in which the nitrogen content is 46% by weight.

4. Iron-nitride-carbide powder the individual particles of which have a carbon content of 1.82% by weight and a nitrogen content of 46% by weight, said iron-nitridecarbide powder being free of a wiron and having the nitrogen content essentially only in the g-iron nitride phase. 7 1

5. A Process for the production of an iron-nitride-carbide powder having a carbon content of 13% by weight and a nitrogen content of 46% by weight which com-' prises mixing iron powder with at least an equal quantity of a finely divided salt component essentially composed of 30 to 100% by weight of alkali metal cyanate and 70 References Cited in the file of this patent UNITED STATES PATENTS 2,036,245 Walter Apr. 7, 1936 2,279,003 Matush Apr. 7, 1942 2,987,429 Smith June 6, 1961 2,994,600 Hansen Aug. 1, 1961 OTHER REFERENCES Lyman: Metals Handbook, 1948 Edition. The American Society for Metals, Cleveland, Ohio, p. 1211. 

1. IRON-NITRIDE-CARBIDE POWDER THE INDIVIDUAL PARTICLES OF WHICH HAVE A CARBON CONTENT OF 1-3% BY WEIGHT AND A MAXIMUM NITROGEN CONTENT OF 7% BY WEIGHT, SAID IRONNITRIDE-CARBIDE POWDER BEING FREE OF A-RION AND HAVING THE NITROGEN CONTENT ESSENTIALLY ONLY IN THE E-IRON NITRIDE PHASE. 